Chapter 5 Transmission Media

Chapter 5Chapter 5GUIDED AND UNGUIDED GUIDED AND UNGUIDED

TRANSMISSION TRANSMISSION MEDIUMMEDIUM

EP301 – Communication System EP301 – Communication System FundamentalsFundamentals

LEARNING OUTCOME:Upon completion of this course,

students should be able to:- 4. Identify the differences between guided and unguided

transmission media using the illustration of its

concept.

Transmission Medium and Physical Layer

TRANSMISSION MEDIUM/ CHANNEL

UNGUIDEDGUIDED

COAXIAL

FIBEROPTIC

TWISTED PAIR

GROUND

WAVESSPACE WAVES

Transmission Medium• Medium is the physical path between

transmitter and receiver – provide connection

• Guided Medium: waves are guided along a solid medium path (twisted pair, coaxial cable, and optical fiber).

• Unguided Medium: waves are propagated through the atmosphere and inner/outerspace (satellite, laser and wireless transmissions).

Transmission Medium – con’t Pair of wires – carry electric signal. Optical fiber – carries the information

on a modulated light beam. Free space – information-bearing

signal is radiated by antenna

1) Twisted Pair CableSeparately insulatedTwisted togetherOften bundled into cablesUsually installed in building during constructionTwists decrease the cross-talk Neighboring pairs have different twist length Most of telephone and network wiring in homes and Offices is TP.

Twisted Pair Cable – con’t

Types of Twisted Pair• UTP (unshielded twisted pair)

– each wire is insulated with plastic wrap, but the pair is encased in an outer covering

• STP (shielded twisted pair)– the pair is wrapped with metallic foil

or braid to insulate the pair from electromagnetic interference

Unshielded and Shielded TP

Unshielded Twisted Pair (UTP)Ordinary telephone wire Cheap, Flexible Easiest to install No shielding Suffers from external EM interference Used in Telephone and Ethernet

Unshielded and Shielded TP

Shielded Twisted Pair (STP) Metal braid or sheathing that reduces interference More expensive Harder to handle (thick, heavy) Used in token rings

Categories of unshielded twisted-pair cables

Category Bandwidth

Data Rate

Digital/Analog Use

1 very low < 100 kbps Analog Telephone

2 < 2 MHz 2 Mbps Analog/digital T-1 lines

3 16 MHz 10 Mbps Digital LANs

4 20 MHz 20 Mbps Digital LANs

5 100 MHz

100 Mbps Digital LANs

5e 100 MHz 100/1000 Mbps Digital LANs

6 250 MHz

1000 Mbps Digital LANs

6a 500 MHz 10 Gbps Digital LANs

Twisted Pros and Cons

• Advantages• a high installed

base • cheap to install • easy to terminate

• Disadvantages:• very noisy • limited in distance • suffers from

interference

Twisted Pair - Applications

• Most common medium• Telephone network

– Between house and local exchange (subscriber loop)

• Within buildings• For local area networks (LAN)

– 10Mbps or 100Mbps

Twisted Pair - Conclusions

• Cheap• Easy to work with• Low data rate• Short range• Speed and throughput 10-100 Mbps• Maximum Cable length 100m

Coaxial cable• Widely installed for use in

business and corporation ethernet and other types of LANs.

• Consists of inter copper insulator covered by cladding material, and then covered by an outer jacket

Coaxial cable – con’t

Outer insulation

Outer conductor (Shield)

Inner insulation (Inner Dielectric Insulator)

Inner conductor (Copper Core)

• Physical Descriptions:

Coaxial cable – con’tCoax Layers

copper or aluminum conductor

insulating material

shield(braided wire)

outer jacket(polyethylene)

Categories of coaxial cables

Category Impedance Use

RG-59RG-59 75 Cable TV

RG-58RG-58 50 Thin Ethernet

RG-11RG-11 50 Thick Ethernet

Coaxial Cable Applications• Most versatile medium• Television distribution

– Cable TV• Long distance telephone transmission

– Can carry 10,000 voice calls simultaneously– Being replaced by fiber optic

• Short distance computer systems links• Local area networks• Maximum cable length 500m in case of Thick

Ethernet and 185 m in Thin Ethernet.• Speed 10-100 Mbps

Coaxial Cable • Advantages• cheap to install • conforms to

standards • widely used

• Disadvantages• limited in distance • limited in number

of connections • terminations and

connectors must be done properly

Optical fiber (or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire.

Fiber Optic Cable

Fiber Optic• Optical fiber is thin (2 to 125 um)• Used to carry signals in the form of light

over distances up to 50 km.• Glasses and plastics can be used to make

optical fibers Optical fiber carries more information

than conventional copper wire. Most telephone company’s long-

distance lines are now of optical fiber.

Fiber Optic Cable – con’t

Fiber Optic Layers

A micron (µm) is equal to one-millionth of a meter. 25 microns are equal to 1/1000 of an inch.

Coating

Three main regions

center: core (9 to 100 microns) middle: cladding (125 or 140 microns) outside: coating or buffer (250, 500 and 900 microns)

Physical Descriptions Of Fiber Optic

CORE This is the light transmission area of the fiber, either glass or plastic. The larger the core, the more light will be transmitted into the fiber.

CLADDINGThe function of the cladding is to provide a lower refractive index at the core interface in order to cause reflection within the core so that light waves are transmitted through the fiber.

COATING/BUFFERCoatings are usually multi-layers of plastic applied to preserve fiber strength, absorb shock and provide extra fiber protection. These buffer coatings are available from 250 microns to 900 microns.

Fiber Optic Cable – con’t

Fiber SizeThe size of the optical fiber is commonly referred to by the outer diameter of its core, cladding and coating. Example:

50/125/250 indicates a fiber with a core of 50 microns, cladding of 125 microns, and a coating of 250 microns. The coating is

always removed when joining or connecting fibers. (A thick of a paper is approximately 25 microns)

Elements in an Optical Fiber Communication

1) Electrical transmit2) Light Source3) Light Source-to-Fiber Coupler4) Fiber Optics5) Fiber-to-detector Coupler6) Light Detector7) Electrical receive

Transmitter

Receiver

Optical Fiber

Basic Elements - con’t

Basic Elements - con’t

Basic Elements of a Fiber Optic Communication System

Analog signal

Electrical Transmit

Light Source Coupler

Encoder

Electrical Receive

Light Detector

Analog signal

Digital signal

Digital signal

TRANSMITTER

RECEIVER

OPTICAL FIBER CABLE

Decoder

Coupler

Repeater

Mode Of Propagation

Optical fibers use light to send information through the optical medium.It uses the principal of total internal reflection.Modulated light transmissions are used to transmit the signal.

Physical Media

Total Internal ReflectionPhysical Media

Fiber Optic Advantages• greater capacity (bandwidth of up

to 2 G bps)• smaller size and lighter weight• lower attenuation• immunity to crosstalk• highly secure due to tap difficulty

and lack of signal radiation

Application of Fiber Optic System

• Telecommunication networks• Military application – aircraft,

ships, tanks,communication links• Closed-circuit TV system used in

building for security• Industrial applications • Medical application/Optometric• Computer

Military application

Computer application

Sensor application

Gas sensorsChemical sensorsMechanical sensorsFuel sensorsDistance sensorsPressure sensors

Medical application

Endoscope Eyes surgery Blood pressure

The FutureFiber Optics have immense potential bandwidth (over 1teraHertz, 1012 Hz) Fiber optics is predicted to bring broadband services to the home

interactive video interactive banking and shopping distance learning security and surveillance high-speed data communication digitized video

Fiber Optics

• Advantages• high capacity • Do not suffer from

electric interference

• can go long distances

• Higher bandwidth and data rates

• Disadvantages• costly • difficult to join• Supports simplex

connection only• Must be handled

with care• Bending is not

easy

Waveguides Waveguide is a conducting tube through which the energy is transmitted, in the form of electromagnetic waves Not carrying a current in the same way as a regular cable. Acts as boundary or enclosure for the space through which the EM wave propagates Waveguide can carry large amounts of high frequency EM energy – can cause eye damage, genetic damage, and other temporary or long- term injury

Warning:• Never look into a waveguide or stand in front of the open

end unless you know that the other end is disconnected

Con’tWhy waveguides? Not cable?• Regular cable cannot effectively

propagate EM energy above 20GHz except for very short distance because or the attenuation caused by skin effect and radiation.

• Cable cannot transfer large amount of power – high voltages will break down the dielectric barrier between conductor

• Impractical for many UHF and microwave applications

Con’t

Waveguide components

Rectangular waveguide

Waveguide to coax adapter

E-teeWaveguide bends

Con’t

Functions Of Waveguide

• To reduce attenuation loss– High frequencies– High power

• Can operate only above certain frequencies– Acts as a High-pass filter

• Normally circular or rectangular– We will assume lossless rectangular

Modes of propagation• TEM (Ez=Hz=0) can’t propagate.

• TE (Ez=0) transverse electric– In TE mode, the electric lines of flux are

perpendicular to the axis of the waveguide

• TM (Hz=0) transverse magnetic, Ez exists– In TM mode, the magnetic lines of flux are

perpendicular to the axis of the waveguide.

• HE hybrid modes in which all components exists

Microstrip Microstrip is a type of electrical transmission line which can be fabricated using printed circuit board technology, and is used to convey microwave-frequency signals

It consists of a conducting strip separated from a ground plane by a dielectric layer known as the substrate

Con’t

A: ConductorC: SubstrateD: Ground planeB: Air

Con’t

Propagation Modes• Mode of propagation of EM

wavesi. Ground-wave propagationii. Sky-wave propagationiii. Space-wave propagation or Line-of-

sight (LOS)

Ground Wave Propagation• Is the component of a transmitted electromagnetic

wave that travels from ground transmitter to ground receiver along the surface of the earth

• These waves may follow the earth’s curvature caused by diffraction and bending and can cover very large areas

Con’t• Also called surface-wave propagation• Dominant mode of propagation• Frequency: below 2MHz (LF)• Applications: AM broadcasting,

maritime radio broadcasting• Disturbances for signal transmission: atmospheric noise, man-made noise,

thermal noise.

Con’t

Sky Wave Propagation• Sky waves are radio waves that

propagate into the atmosphere and then are returned to earth at some distance from the transmitter

• Transmitted signals being reflected from ionosphere

Con’t• Frequency : 2-30 MHz (HF)• Little loss• Problem : Signal Multipath• Application : amateur radio and long

distance aircraft and ship communication.

Con’t

Antenna at different angles

> fc

Space Wave Propagation• are radio waves that travel directly

from the transmitting antenna to the receiving antenna

• It travel in straight lines (called Line of Sight)

• Frequency: 30-300MHz (VHF) 0.3 – 3GHz

• Application: mobile phones, FM two-way radio,TV and radar.

Con’t

Propagation Modes

Con’t

Con’t

Con’t

Satellite Communication Concepts

Satellite is defined as a man-mad vehicle that orbits the earth

Specialized wireless receiver/ transmitter that is launched by a rocket and placed in orbit around the earth

Satellite Communication System is a system that uses orbiting vehicles to relay radio transmission between earth terminals

Con’tTypes of satellite:

1)Passive – simply reflects radio signal back to earth

2)Active – acts as repeaters, it amplifies the signal received and then transmit them back to earth

Transmitter transmits to the satellite on a frequency called uplink frequency.

Satellite amplifies the signal and transmits back to receiver on a frequency called downlink frequency

Satellite Frequency Bands

BAND FREQUENCY RANGE (GHz)L 1-2 (MSS)S 2.5 – 4 (MSS,NASA)C 3.7 – 8 (FSS)X 7.25 – 12 (military)Ku 12 – 18 (DBS)Ka 18 – 30.4 (FSS)V 37.7 – 50.2 (FSS)

Different kinds of satellites use different frequency bands.

FSS = Fixed Satellite ServiceMSS = Mobile Satellite ServiceDBS = Direct Broadcast Satellite

Con’t

• The most common carrier frequencies used are C-band (6/4 GHz) and Ku-band (14/11 GHz) especially for voice, video and data telecommunications

• ITU has allocated the 60GHz band for intersatellite links ( satellite-to- satellite)

Advantages of SCS• It can access to wide geographical area• Higher Bandwidths are available for use • Transmission cost of a satellite is

independent of the distance from the center of the coverage

• Satellite to satellite communication is very precise

Limitations of SCS• High initial cost –launching cost• Has propagation delay• Satellite bandwidth is gradually

becoming used up

Applications of SCS• Digital audio broadcasting• Television distributions• Servicing remote areas• Remote monitoring and control• Vehicle tracking• Mobile communications• Maritime and air navigation• Video teleconferencing

Antenna•They convert electrical signals on wires intoradio waves and vice versa.

•An antenna must be made of conducting material. Radio waves hitting an antenna cause electrons to flow in the conductor and create a current.

• Likewise, applying a current to an antenna creates an electric field around the antenna. As the current to the antenna changes, so does the electric field. A changing electric field causes a magnetic field.

ANTENNA PROPAGATION

An electromagnetic wave is created by a local disturbance in the electric andmagnetic fields.  From its origin, the wave will propagate outwards in all directions.If the medium in which it is propagating (air for example) is the same everywhere,the wave will spread out uniformly in all directions.

TYPES OF ANTENNA

Directional This type of antenna does not offer any

added power to the signal, and instead simply redirects the energy it received from the transmitter. By redirecting this energy, it has the effect of providing more energy in one direction, and less energy in all other directions

Yagi- better suited for shorter links

- lower dBi gain; usually between 7 and 15 dBi

Parabolic- used in medium to long links

- gains of 18 to 28 dBi

- most common

Omni-Directional• An omnidirectional antenna is

designed to provide a 360 degree radiation pattern

• This type of antenna is used whencoverage in all directions from the

antennais required.

Omni- used at the CCU or Master NCL for wide coverage

- typical gains of 3 to 10 dBi

END OF CHAPTER 5END OF CHAPTER 5